In recent years, self-propelled agricultural harvesting machines have been equipped with more and more powerful internal combustion engines that can currently output, in the case of forage harvesters, up to 800 kW. Due to the relatively small number of such powerful engines produced, these engines are relatively expensive and usually more expensive than two internal combustion engines that each have half the power. Furthermore, the entire power of the engine is not always needed—for example, it is usually not needed during transport on a street or while mowing. This leads to poorer efficiency of the engine than during full-load operation, which is why it was proposed, e.g., in European Patent Application EP 1 640 201 A1 to equip a self-propelled harvesting machine with two internal combustion engines of which one can be added to the other internal combustion engine for handling greater power requirements. Consequently, the first internal combustion engine is always in operation, while the second internal combustion engine is turned on only when needed. In the single-engine mode, the power of an individual internal combustion engine is available, and in the double-engine mode, the power of both internal combustion engines is available, i.e., twice the power. The maximum available power from the individual internal combustion engines is the same in both operating modes. Similar arrangements are also used in airplanes and buses, e.g. German Patent Documents DE 69 49 295 U1 and DE 37 41 891 A1, respectively. The mentioned harvesting machines are also available on the market with internal combustion engines of different powers, wherein the first internal combustion engine has the greater power.
There are certain operating conditions in which the power of a single internal combustion engine is not sufficient, for example, while harvesting a relatively thin crop or while in transport with a towed harvesting attachment when a steep incline is to be climbed. One could indeed equip the work machine with one or two internal combustion engines of greater power, but in the case of the double-engine mode, this would again have the result that the other components of the work machine, in the case of a harvesting machine, for example, the drive train for driving crop-processing devices and the devices themselves would have to be designed larger. In many cases, however, this measure is undesirable for reasons of cost and/or weight. The known solution with a larger primary engine and a smaller secondary engine that can be connected is disadvantageous in so far as the primary engine experiences significantly greater wear.